Silicone resins have been used for a number of purposes because of their thermal stability, dielectric properties, chemical stability and resistance to atmospheric deterioration. The recently published papers, "Electrical Performance and Reaction Kinetics of Silicone Gels," C. P. Wong, Journal of Material Research, Vol. 5, No. 4, April 1990, pp. 795-800, and, "Understanding the Use of Silicone Gels for Nonhermetic Plastic Packaging," C. P. Wong et al., IEEE Transactions on Components, Hybrids, and Manufacturing Technology, Vol. 12, No. 4, December 1989, pp. 421-425, describe the use of silicone resins as encapsulants for electronic devices, particularly integrated circuits.
The patent of Wong, U.S. Pat. No. 4,888,226, granted Dec. 19, 1989, is directed to a silicone resin that is particularly suitable for wire bonded hybrid integrated circuits. A hybrid integrated circuit is one in which a semiconductor chip, usually a silicon chip, is connected to a bonding pad region of a circuit pattern on a ceramic substrate. However, subsequent studies have indicated that, with ever higher requirements on the dependability of integrated circuits, the formulations of the Wong patent are still not as reliable as is desired. Particularly under extreme conditions of temperature and humidity, and with high integrated circuit bias voltages, failures of complex integrated circuits may still occur. With certain complex and high bias circuits, more protection is required since only a small amount of corrosion of a conductor can cause a failure of such circuits. There is therefore a continuing need for integrated circuit encapsulants that give a higher degree of protection from outside contaminants, particularly under conditions of high temperature and humidity, together with high voltage or current conduction in the encapsulated integrated circuit.